1. Field of Invention
This invention relates to a new and improved signal system for use with measuring sensor/transducers of the variable impedance type.
More particularly, the invention relates to a signal amplifier system for improved processing of the voltage signal developed by a sensor/transducer used to measure certain physical parameters such as displacement, force, torsion, temperature, size, pressure, vibration and the like. The physical parameter to be measured causes a variation in the impedance of one of the elements of the sensor transducer which in turn is used to vary the pulse rate of the signals generated by the system. The pulse rate is indicative of the physical parameter being measured.
2. Description of the Prior Art
Many types of physical parameters such as displacement, size, pressure, force, tension, vibration and the like may be determined by measuring the spacing between two elements, at least one of which shifts with respect to the other in accordance with the parameter of interest. If the two elements are, or can be made metallic then they can be treated as forming a variable impedance with a capacitance indicative of the spacing between the elements. Thus the spacing may be determined by measuring the impedance (or capacitance) of the elements.
However, because of certain fringe effects and other stray capacitance between any two elements, it was difficult to devise a variable impedance type measuring system in which a linear output could be obtained. One such system is disclosed in commonly assigned U.S. Pat. No. 4,067,225 entitled CAPACITANCE TYPE NON-CONTACT DISPLACEMENT AND VIBRATION MEASURING DEVICE AND METHOD OF MAINTAINING CALIBRATION, granted on Jan. 10, 1978 to Richard A. Dorman et al. An amplifier system using the variable impedance sensor/transducer of said U.S. Pat. No., 4,067,225 to generate an A.C. signal indicative of a physical parameter of interest by modulating the output of a carrier oscillator is disclosed in a commonly assigned U.S. Pat. No. 4,176,555 entitled SIGNAL AMPLIFIER SYSTEM FOR CONTROLLED CARRIER SIGNAL MEASURING SENSOR/TRANSDUCER OF THE VARIABLE IMPEDANCE TYPE, granted on Dec. 4, 1979 to Richard A. Dorman.
Frequently, it is necessary or desirable to use the measurements obtained from a sensor/transducer in an automatic signal processing or monitoring system. It was found that if this latter signal processing or monitoring system is adapted to handle digital signals then auxiliary interfacing systems must be provided for analog-to-digital conversion and conditioning of the AC signals generated by the device described in the above-mentioned U.S. Pat. No. 4,176,555. It is well known that such auxiliary systems invariably delay the signals and therefore reduce the overall response time of the monitoring system. In addition, analog-to-digital data conversion is accompanied by quantization and other types of errors which degrade the overall resolution and accuracy of the system.